Create a new folder link to automatically route documents to a folder.

    You must provide either a `user` ID or phone number information. For phone numbers,
    you can provide:
    
    1. **Existing phone number**: Use `phone_number` field with a hashid string
    2. **New phone number**: Use `phone_number` field with a dictionary containing `raw_number`
    3. **Alternative format**: Use `phone_number_data` field with phone number details
    
    When creating a new phone number, you can optionally include `person` data to create
    a person record associated with that phone number.
    
    **Examples:**
    
    Link to existing user:
    ```json
    {
      "folder": "folder_hashid",
      "user": 123
    }
    ```
    
    Link to existing phone number:
    ```json
    {
      "folder": "folder_hashid", 
      "phone_number": "phone_hashid"
    }
    ```
    
    Create new phone number with person data:
    ```json
    {
      "folder": "folder_hashid",
      "phone_number": {"raw_number": "+15551234567"},
      "person": {
        "preferred_name": "John Doe",
        "email_address": "[email protected]",
        "role": "CLIENT",
        "allows_email": true
      }
    }
    ```